Modern tactical aircraft use a number of imaging aids to view external objects/scenes; and visible, infrared and/or narrow-spectrum optical devices are used in various applications to form an image of a scene. Real-time acquisition of high-resolution, wide field of regard and high dynamic range images is essential for many military and civilian surveillance applications. In order to achieve a wide field of regard, an imaging device may be mounted on a gimbal, with a steering subsystem being provided to enable the imaging device to be steered to cover a required field of view. In order to achieve long range imaging, relatively large optical systems (i.e. long focal length and large sensing aperture) are required; and in all cases, the imaging components, which tend to be bulky and complex, are affixed to the host platform, which makes a significant contribution to the overall size, weight and power associated with the host platform subsystems.